Microbiology & Virology

Microbiology & Virology

In normal form, DNA helix is?

Under physiological conditions DNA adopts B-form, a right-handed double helix with antiparallel strands stabilized by Watson-Crick base pairing and base stacking. Ten base pairs per turn produce major and minor grooves crucial for protein interactions.

Ref: Watson JD and Crick FHC, Molecular Structure of Nucleic Acids, Nature 1953, and Alberts B et al., Molecular Biology of the Cell, 6th Edition, Chapter 4 DNA Structure and B-Form Helix, describes B-DNA as right-handed double helix with complementary pairing, published by Garland Science.

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Microbiology & Virology

All of the following codons terminate protein biosynthesis EXCEPT:

Standard termination codons UAA, UAG and UGA lack cognate tRNAs and recruit release factors to stop translation. UUA encodes leucine, recognized by tRNA-Leu, so does not terminate protein synthesis and is incorporated into growing polypeptide chain.

Ref: Nelson DL and Cox MM, Lehninger Principles of Biochemistry, 7th Edition, Chapter 27 Protein Metabolism and Genetic Code, discusses genetic code table, stop codons UAA UAG UGA function and leucine codon UUA coding property, published by W H Freeman.

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Microbiology & Virology

In gene cloning, the term vector refers to:

Cloning vectors are plasmids containing origin of replication, selectable marker and multiple cloning site. They replicate autonomously in host bacteria, carrying foreign DNA inserts for amplification, expression or sequencing, essential tools in recombinant technology.

Ref: Sambrook J and Russell DW, Molecular Cloning: A Laboratory Manual, 4th Edition, Chapter 4 Plasmid Vectors and Cloning Vehicles, defines vectors as vehicles carrying foreign DNA, describes essential features and cloning applications, published by Cold Spring Harbor Laboratory Press.

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Microbiology & Virology

What is central dogma?

Central dogma proposed by Crick states genetic information flows from DNA via transcription to mRNA, then via translation to protein. This directional transfer underlies gene expression, though reverse transcription and prion exceptions modify classical view.

Ref: Crick FHC, Central Dogma of Molecular Biology, Nature 1970, and Alberts B et al., Molecular Biology of the Cell, 6th Edition, Chapter 6 How Cells Read Genome, discusses DNA to RNA to protein information flow and mechanisms, published by Garland Science.

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Microbiology & Virology

Okazaki fragments are formed on:

Lagging strand synthesis is discontinuous because DNA polymerase moves only 5' to 3' opposite fork progression. Short Okazaki fragments initiated by RNA primers are synthesized, later joined by ligase, ensuring continuous replication of antiparallel duplex.

Ref: Alberts B et al., Molecular Biology of the Cell, 6th Edition, Chapter 5 DNA Replication Mechanisms and Okazaki Fragments, explains leading versus lagging strand synthesis, fragment formation and RNA primer removal, published by Garland Science.

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Microbiology & Virology

The coding sequences of a gene are called:

Eukaryotic genes comprise exons that remain after splicing and encode amino acids, interspersed with noncoding introns removed by spliceosome. Alternative splicing of exons increases proteomic diversity from single locus, central to gene expression regulation.

Ref: Watson JD et al., Molecular Biology of the Gene, 7th Edition, Chapter 12 RNA Splicing and Processing, describes exons as coding sequences, intron removal, spliceosome mechanism and alternative splicing significance, published by Pearson Education.

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Microbiology & Virology

SSP-PCR is:

SSP-PCR uses primers designed complementary to specific allelic sequences, amplifying only when target polymorphism present. It enables low-resolution HLA typing, SNP detection and pathogen genotyping rapidly without sequencing, relying on precise primer-template matching.

Ref: Erlich HA et al., PCR Technology: Principles and Applications, Chapter on Sequence Specific Primer PCR, explains SSP-PCR design, allele specific amplification, primer specificity and applications in HLA typing and immunogenetics, published by Oxford University Press and Stockton Press.

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Microbiology & Virology

Weakness of hydrogen bonding between bases in sticky ends are stabilized by a process called as:

Restriction enzymes create complementary sticky overhangs held only by few hydrogen bonds, unstable alone. DNA ligase catalyzes phosphodiester bond formation between adjacent 3'-hydroxyl and 5'-phosphate, covalently sealing nicks and stabilizing recombinant molecules.

Ref: Brown TA, Gene Cloning and DNA Analysis: An Introduction, 7th Edition, Chapter 2 Vectors and Essential Techniques, discusses sticky ends, hydrogen bonding weakness and ligase-mediated phosphodiester bond formation for recombinant stability, published by Wiley Blackwell.

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Microbiology & Virology

Western blotting is the technique used for identification of:

Western blot separates proteins by SDS-PAGE, transfers onto nitrocellulose membrane, and detects via specific primary antibodies and enzyme-conjugated secondary antibodies. It confirms protein identity, size and post-translational modifications, essential for HIV diagnosis.

Ref: Alberts B et al., Molecular Biology of the Cell, 6th Edition, Chapter 8 Analyzing Proteins and Immunoblotting Techniques, details SDS-PAGE, western blotting technique, antibody detection and protein analysis applications, published by Garland Science.

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Microbiology & Virology

Line probe assay (LiPA) is based on:

LiPA employs reverse hybridization where amplified biotinylated DNA hybridizes to specific oligonucleotide probes immobilized on nitrocellulose strips. Line patterns reveal mutations, used extensively for Mycobacterium tuberculosis drug resistance and HLA typing with high specificity.

Ref: Persing DH et al., Molecular Microbiology: Diagnostic Principles and Practice, 3rd Edition, Chapter 6 Reverse Hybridization and Line Probe Assays, describes line probe assay principle, probe immobilization, detection of mutations and clinical applications, published by ASM Press.

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Microbiology & Virology

Emulsification of fats is carried out by:

Bile salts are amphipathic derivatives of cholesterol that reduce surface tension, breaking large fat globules into micelles. This emulsification increases lipase accessibility, facilitating triglyceride hydrolysis and absorption of fatty acids and fat-soluble vitamins in duodenum.

Ref: Nelson DL and Cox MM, Lehninger Principles of Biochemistry, 7th Edition, Chapter 10 Lipids and Chapter 17 Fatty Acid Metabolism, covers bile salts structure, emulsification function, micelle formation and lipid digestion mechanism, published by W H Freeman.

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Microbiology & Virology

Arneth count is used to count:

Arneth count classifies neutrophils based on number of nuclear lobes, reflecting age distribution. Left shift indicates increased immature bilobed forms during acute infection, while right shift shows hypersegmented neutrophils in megaloblastic anemia or chronic disease.

Ref: Hoffbrand AV and Moss PAH, Hoffbrand's Essential Haematology, 7th Edition, Chapter 17 White Blood Cells and Leukemias, explains Arneth count, neutrophil nuclear segmentation, left and right shift clinical significance, published by Wiley Blackwell.

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